Pixelised GIFs
Here's a neat little effect I discovered quite by chance.
Take any small, animated GIF and increase its dimensions in the HTML <img ...> tag. The result is a neat, pixelised animation like the one below.
I have experimented a little with this and it is effective with most animations, the optimum effect seems to be achieved when the image width and height tags are around 3x their actual values. Thus, if your animation is 100x100 pixels in size, you should be able to scale it up to 300x300 pixels.
A neat side-effect of this technique is that you can have "large" animations on your pages, yet small file-sizes (and download times).